Decreased urine output does not necessarily mean that the kidneys are bad, there are other factors. Normal human daily urine volume is about 1000-1500ml, if the 24-hour urine volume is less than 400ml, it is considered as oliguric state in medical science. Causes of oliguria: First, physiological reduction. If you drink too little water or sweat more and lose more body fluids, at this time the kidney filtration is reduced and the urine volume is reduced, not less urine due to kidney insufficiency. If you drink more water or rehydration, the urine volume can return to normal. Second, post-renal obstruction. That is, the kidney filtration function is normal, but with diseases such as urethral stones or prostatic hyperplasia, resulting in urethral blockage, the urine filtered by the kidney is retained within the kidney, ureter and bladder, and cannot be discharged through the urethra. In this case, the obstruction should be lifted and the urine volume can be restored to normal. Third, nephrogenic oliguria. This kind of situation belongs to the kidney insufficiency or bad kidney caused by less urine, because of various diseases, such as glomerulonephritis and nephrotic syndrome caused by the destruction of kidney function, filtration is reduced, the urine volume is reduced at this time.